The present invention relates to a method of fabricating a semiconductor device, particularly, a method of forming one or more contact holes in an interlayer insulating film of a semiconductor device.
A semiconductor device requires smaller design rule in order to have higher operational speed and lower electrical consumption. Therefore, it is required that a contact hole in an interlayer insulating film of a semiconductor device should have a smaller diameter. For example, a contact hole in an interlayer insulating film of a semiconductor device of 100 nm node generation needs to have a diameter of approximately 0.16 μm as the smallest contact hole size.
In general, a contact hole is formed by the steps of forming a resist layer on an interlayer insulating film, forming an opening in the resist layer using photolithography, and etching the interlayer insulating film using the resist layer as a mask. However, an expensive apparatus must be used for forming a mask based on the smallest design rule in order to reduce a diameter of a contact hole, thereby increasing the manufacturing cost of a semiconductor device. For example, Japanese Patent Kokai (Laying-open) Publication No. 05-226278, especially, its FIG. 3, discloses a side wall disposed inside an opening passing through a resist layer and an interlayer insulating film for reducing a diameter of a contact hole.
The side walls make it possible to reduce diameters of plural openings passing through a resist layer and an interlayer insulating film by the same value. Therefore, a process using the side walls is suitable for forming plural contact holes with the same diameter simultaneously, but is not suitable for forming plural contact holes with different diameters simultaneously. Furthermore, when forming plural contact holes with different diameters simultaneously using the side walls, diameters of plural openings passing through a resist layer must have different values. However, there is a problem that dimensional error tends to be increased in the openings with a diameter different from a diameter of a target opening in an exposure process of the resist layer.